Solid polymer electrolyte fuel cells (hereinafter referred to as PEFCs) are devices wherein a fuel gas containing hydrogen and an oxygen-containing oxidizer gas, such as air, are caused to react electrochemically with each other, thereby generating electric power and heat simultaneously.
In general, PEFCs each have a structure wherein plural cells are laminated onto each other. Any one of the cells has a structure wherein a membrane-electrode assembly (hereinafter referred to as an MEA) is sandwiched between a pair of plate-form conductive separators, specifically, an anode separator and a cathode separator. The MEA is equipped with an MEA principal part, and a frame arranged to extend over a circumferential region (or the periphery) of the MEA principal part and further surround the MEA principal part. Herein, the MEA equipped with the frame is referred to as an electrode-membrane-frame assembly.
The MEA principal part includes a polymer electrolyte membrane the circumferential region of which is supported by the frame, and paired electrode layers that are formed on both surfaces of the polymer electrolyte membrane, respectively, and are further arranged inside the frame. The paired electrode layers include catalyst layers of platinum or the like that are formed on both surfaces of the polymer electrolyte membrane, respectively, and porous, conductive gas diffusion layers formed on the catalyst layers, respectively. When a fuel gas and an oxidizer gas contact the paired electrode layers, respectively, electrochemical reaction is generated to generate electric power and heat. In the meantime, a gasket is set up on a surface of the frame to seal gaps between the surface and the separators, and the gasket blocks or restrains a leakage of the fuel gas and the oxidizer gas to the outside.
Hereinafter, a process of a first conventional example for producing an MEA will be described. FIG. 20A to FIG. 20D are schematic explanatory views illustrating the process of the first conventional example for producing an MEA, wherein a joint region between an MEA principal part and a frame is enlarged and shown.
As illustrated in FIG. 20A, a first mold T101 and a second mold T102 are clamped to each other to mold a primary molded body 106A constituting a portion of a frame 106.
Thereafter, the second mold T102 is removed. As illustrated in FIG. 20B, an MEA principal part 105 is arranged into a depression T101A in the first mold 1101, the part 105 being a part wherein paired electrode layers 105D are formed on both surfaces of a polymer electrolyte membrane 105A, respectively, and inside a circumferential region of the polymer electrolyte membrane 105A. At this time, the circumferential region 105E of the MEA principal part 105 is arranged on a flat region T101B of the first mold T101 and a flat region 106A1 of the primary molded body 106A.
Next, as illustrated in FIG. 20C, the first mold T101, wherein the MEA principal part 105 is arranged, and a third mold T103 are clamped to each other so as to mold a secondary molded body 106B constituting the other portion of the frame 106. In this way, the primary molded body 106A and the secondary molded body 106B are integrated with each other to form the frame 106.
Next, from the first mold T101 and the third mold T103, the MEA principal part 1105, to which the frame 106 is joined, is taken out, and the workpiece is arranged between a fourth mold T104 and a fifth mold T105. Next, as illustrated in FIG. 20D, the fourth mold T104 and the fifth mold T105 are clamped to each other, and then a gasket 107 is molded onto a surface of the frame 106.
In the MEA having a structure as described above in the first conventional example, the following region is present between the electrode layers 105D and the frame 106: a region where the polymer electrolyte membrane 105A is alone present, that is, a region of the polymer electrolyte membrane 105A that is neither supported by the electrode layers 105D nor the frame 106. Therefore, from a viewpoint of handling, and from a viewpoint of preventing the polymer electrolyte membrane 105A from being broken by a difference in pressure between fuel gas and oxidizer gas or by some other cause when the fuel cell is driven, the polymer electrolyte membrane 105A positioned between the electrode layers 105D and the frame 106 is reinforced. Techniques for such reinforcement are disclosed in, for example, Japanese Patent No. 3368907 and Japanese Patent No. 3897808.
FIG. 21A to FIG. 21D are schematic explanatory views illustrating a process of a second conventional example for producing an MEA, disclosed in Japanese Patent No. 3368907, wherein a joint region between an MEA principal part and a frame is enlarged and shown. As illustrated in FIG. 21A to FIG. 21D, in the MEA in the second conventional example, a reinforcing membrane 108 is set into a picture frame form over the circumferential region 105E of an MEA principal part 105 to reinforce a polymer electrolyte membrane 105A, and then a frame 106 and a gasket 107 are molded.
FIG. 22A to FIG. 22D are schematic explanatory views illustrating a process of a third conventional example for producing an MEA, disclosed in Japanese Patent No. 3897808, wherein a joint region between an MEA principal part and a frame is enlarged and shown. As illustrated in FIG. 22A to FIG. 22D, in the MEA of the third conventional example, sixth and seventh molds T106 and T107 are used instead of the fourth and fifth molds T104 and T105. In this way, a gasket 107A is molded to cover a polymer electrolyte membrane 105A positioned between electrode layers 105D and a frame 106, so as to reinforce the polymer electrolyte membrane 105A.
However, according to the technique of the second conventional example, wherein the reinforcing membrane 108 is set up, the number of parts naturally increases, and further the number of steps for the production increases. Furthermore, when the reinforcing membrane 108 is formed by, for example, punching-out in order to form the reinforcing membrane 108 into a picture frame form, the punched-out region is lost, and others are caused. Thus, disadvantages in costs are caused.
The technique of the third conventional example, wherein the gasket 107A is molded, causes the following: at the time of causing a material which is to constitute the gasket 107A, for example, a thermoplastic resin to flow into the molds T106 and T107, pressures applied to both surfaces of the polymer electrolyte membrane 105A may become uneven. Therefore, as represented by a region surrounded by a broken line in FIG. 23, the polymer electrolyte membrane 105A deforms (for example, it becomes wavy). It is therefore necessary to raise a precision of the molds T106 and T107, or control the resin pressures strictly in order to restrain the deformation.